Home Fruit and. Vegetable Dehydration E. H. WIEGAND THOMAS ONSDORFF. ALYCE HOLMES

Transcription

1 STATION CIRCULAR 149 APRIL 1943 Home Fruit and Vegetable Dehydration E. H. WIEGAND THOMAS ONSDORFF. ALYCE HOLMES Oregon State System of Higher Education Agricultural Experiment Station Oregon State College Corvallis

2 TABLE OF CONTENTS Page Dehydration Principles 3 Selecting the Fresh Product 6 Importance of Proper Preparation 8 Preparation -of Fruits for Dehydration 8 Preparation of Vegetables for Dehydration 9 Operating the Dehydrator 11 Packing and Storage of Dehydrated Products 12 Preparation of Dehydrated Foods for Co9king 14

3 R Home Fruit and Vegetable Dehydration E. H. WIEGAND,1 THOMAS ONSDORFF,' and ALYCE HOLMES3 ESTRICTIONS that are being imposed in order to conserve essential materials for war needs make it imperative that methods of food preservation other than canning be adapted to assist in building up adequate food supplies. Many families are not in a position to can yegetables properly, because pressure cookers are not available. Glass jars, rubber jar rings, and many of the other accessories to canning are becoming scarce. The army, the navy, and the lend-lease program are taking large volumes of our commercially packed foods, making some of the important food items hard to obtain. The Victory Garden Campaign will increase the raw material supply to most families, and provision should be made by these families to preserve the surpluses from their gardens. Where pressure cookers are not available to preserve these surplus vegetables, a simple small drying unit, used to conserve these products, can be made or obtained at a nominal cost. DEHYDRATION PRINCIPLES The fundamental principle of preservation by drying is that of moisture reduction. When fresh fruits or vegetables contain their normal amounts of water, they are subject to spoilage. Removing this moisture preserves the material, because it removes the principal element necessary for the growth of organisms, such as yeasts, molds, and bacteria. To remove moisture from fresh products, it is necessary to supply energy in the form of heat. This heat energy changes the water in the fruit or vegetable to a vapor that is carried away by the circulating air, These changes can be accomplished with such heating devices as those indicated in Circular of Information 309, "Construction and Operation of a Home Electric Food Dehydrator." All evaporation processes are dependent on three factorsheat, circulation, and humidity (or moisture) present in the air. Heat then furnishes the energy to evaporate the water. The dryness of the air partly governs the rate of evaporation, and circulation further as - sists by carrying off the water vapor. ifood Teehnologist in Charge. Food Industries Department. 5Associate Food Technologist, Food Industries Department. 'Research Assistant. Food Indu tries Department.

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6 AGRICULTURAL EXPERIMENT STATION CIRCULAR 149 The small home dehydrator is so constructed that all these principles are ingeniously incorporated. Thus with a unit of this type, if the temperature is maintained at from 1500 to 155 F., drying will proceed rapidly and the products will be properly dried. All products, when first placed in the dehydrator, give up their moisture freely. Later when the moisture in the product is reduced to less than half, the rate of evaporation is materially reduced. This slowing up of the drying rate is due principally to the loss of liquid from the cells that slows up the flow of the moisture from the interior of the fruit or vegetable. Sliced or cut products will give up their moisture more freely than whole products. All raw products tend to resist excessive evaporation because the cells are still alive and active. After ing, the cells lose their ability to resist and water passes through more freely. This is indicated in ed vegetables: Where whole fruits like prunes or cherries are dried, many hours of heating are necessary to reduce the moisture content to a safe preserving point. Here the outer skin tissue tends to slow down evaporation. As temperature is the most important controlling factor, it should be maintained at 150 to 155 F. to insure rapid evaporation. Higher temperatures than this tend to impair the quality of the finished product. When operating the dehydrator, be sure to maintain the temperature as close to F. as possible. SELECTING THE FRESH PRODUCT To insure success in the finished product, select fresh fruit or vegetables of good quality. Use only ripe fruit that has reached its full development and is in prime eating condition. Vegetables that are mature but still tender and succulent should be used. Overmature vegetables tend to be tough, stringy, and flavorless. Varieties recommended for use in freezing are usually suitable for dehydration. Early morning harvest of vegetables while the products are fresh and succulent is recommended. Rapid handling then will conserve vitamins ordinarily lost through long holding and storage. Under no conditions should succulent vegetables be held longer than 6 hours after harvest before drying, and it is essential they be kept cool during this time. Make your dehydration plans to supply a variety of those fruits and vegetables that will provide the greatest amount of nutritive material. Your selection of foods should include items that will give variety in color and flavor, as well as nourishment.

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8 8 AGRICULTURAL EXPERIMENT STATION CIRCULAR 149 IMPORTANCE OF PROPER PREPARATION Fresh fruit and vegetables contain many nutritive substances that are easily lost in storage, handling, and preparation. Conservation of these is important. Chief among these elements are vitamins, sugars, proteins, and mineralsall essential to the body. When preparing the products, certain steps are necessary to conserve some of these essential materials. Many, like Vitamin C, oxidize readily in the presence of.air. Others, like sugar and minerals, dissolve in the washing or ing procedure and are lost. With greater care given to each step in the preparation, more of these elements can be retained in the product. PREPARATION OF FRUITS FOR DEHYDRATION Washing is the first step in preparation. After cleaning, some fruits, like apples, are hand-peeled, cored, and sliced. Others, such as apricots, are cut in half and the pit is removed. Peaches are usually cut, halved, and pitted. Peeling is optional; if peaches are sliced, they should be peeled. Peeling such fruits as peaches is easily accomplished by immersing a small quantity of fruit in quite a large volume of boiling water. After the fruit is immersed in this water for 1 to 1 minutes, dip in cold water to cool. The skin of properly ripened fruit will slip readily. Longer immersion may be needed for underripe fruit. Suiphuring fruit. Fruit that is sliced or cut is most subject to oxidation or discoloration because the soft tissue is exposed. Oxidation is caused by enzymes and the oxygen of the air coming into contact with the cut surfaces of the fruit. As soon as the fruit is peeled or sliced, the cut surfaces should be temporarily protected. This can be done best by dipping the product in a weak salt solution (approximately 3 tablespoons per quart of water). Best protection during the drying process is afforded the product by subjecting the fresh cut fruit to the fumes of burning sulphur. This treatment will also afford protection against insects to the dry fruit in storage. All highly acid fruit that tends to oxidize or discolor readily, needs to be sulphured and must not be dried on wire-screen trays. To safeguard the product, use only wood-slat trays. Sulphuring takes from 30 minutes to 2 hours for most fruit products. (See Table 1.) Pears, peaches, and apricots can, however, be subjected to these fumes (sulphur dioxide) for as long as 8 hours without injury. Long suiphuring bleaches the color, which will return as the product dries. The sulphur absorbed by the fruit

9 HOME FRUIT AND VEGETABLE DEHYDRATION acts as a preservative, as well as an antioxidant, and is almost completely driven off when the product is cooked. PREPARATION OF VEGETABLES FOR DEHYDRATION In general, the preparation of vegetables for dehydration is not different from their preparation for any other home use. Precautions should be taken to see that the pieces of the prepared product are of uniform thickness as indicated for that product in Table 1. Blanching is the most important step in the preliminary treatment of vegetables. If the products are not thoroughly ed, they will not retain their flavor, color, or nourishing qualities. All fresh, uncooked vegetables contain quantities of enzymes. These enzymes are complex organic substances that cause changes in living tissue. They are present and active during the life of the vegetable and coitinue to function in breaking down plant materials unless they -are inactivated, Blanching is the most practical process by which we can stop the action of enzymes that produce off flavors and odors during storage and make the dehydrated products undesirable for consumption. Figure 4. Blanching vegetables by steaming method. Small batches are necessary to insure thorough heat distribution. Note steam escaping due to pressure generated.

10 10 AGRICULTURAL EXPERIMENT STATION CIRCULAR 149 The ing can be accomplished with the use of steam or hot water. is often hard to obtain in quantity. The use of large 4 to 6 gallon cookers or soup stock pots in which a large flat area of water can be heated quickly will materially assist in the formation of steam. Construct a wire basket that will fit the cooker and can Figure 5. Spread ed vegetables while still hot.

11 HOME FRUIT AND VEGETABLE DEHYDRATION 11 be suspended above the water. Cover the bottom of the cooker with about 2 inches of boiling water. Place enough prepared vegetable material to fill one tray only, or not more than 1 inches of vegetables in the basket at one time. Support the basket on a wire rack in the steam above the boiling water, closing the lid tightly. When a light pressure is formed, indicated by the pressure of escaping steam from below the lid, the ing of the vegetables will proceed quickly. The time of ing, after pressure is created, is governed by the product and its compactness. (See Table 2.) It is recognized that steam ing will be somewhat slower than hot water ing. This is due to the lack of distribution of heat through the cold vegetables. Hence for steam ing not more than 1 inches of vegetables should be placed in the basket. Batches of vegetables will more quickly in hot water because of the quicker distribution of heat. When hot water is used as a ing medium, use a large vessel as indicated under steam ing. Fill vessel at least half full of water. Place on largest burner to supply heat quickly. Bring water to a vigorous boil. Place enough vegetables for one tray in the wire basket, submerge in boiling water, and agitate by stirring gently or by raising and lowering the basket during ing. (Refer to Table 2 for exact ing time.) It must be recognized that large quantities of water drop less in temperature than small quantities when the cold vegetables are introduced. It becomes evident, therefore, that the use of a large vessel for ing in. hot water is imperative. Before ing another basket of vegetables, be sure the water has again come to a vigorous boil. OPERATING THE DEHYDRATOR Some time before starting the drying operations, heat up the dehydrator. By the time the fruit or vegetables are prepared, the dehydrator should be up to a temperature of l5o01550 F. After ing, spread the hot vegetables on the tray immediately and place in the preheated dehydrator. It is important when operating the dehydrator to have the prepared ed material go into the unit as hot as possible. This will prevent too great a fluctuation in the temperature of the drying unit. To dehydrate fruits or vegetables quickly, careful attention should be given to the following items: 1. The temperature of the dehydrating unit should be established at 1500 to 1550 F. Check the temperature of the unit at regular intervals to see that it is maintained throughout the drying period.

12 12 AGRICULTURAL EXPERIMENT STATION CIRCULAR The, sliced fruit and vegetable load should never exceed 1 pound per square foot of tray surface. Spread the material evenly on the trays to prevent wet spots (2 to 3 pounds per tray for home dehydrator illustrated in Circular of Information 309). Figure 6. Load trays carefully with proper amount of raw materials. Spread evenly on tray to insure uniform drying. Note spread and effect in illustration. The spread where halved fruit is used should not exceed 1 to 2 pounds per square foot of tray surface (3 to 5 pounds per tray for home dehydrator illustrated in Circular of Information 309). Maintain heat constantly at temperature indicated above. For the best results fill dehydrator gradually. Reverse trays from end to end if necessary to assist drying. Dry fruit until it loses enough moisture to become leathery. (See Table 1. If in doubt, dry further.) The center of the piece, when broken, should show no free moisture. Dry vegetables until they lose enough moisture to become brittle and snap sharply in two when bent. Make test only after the vegetable has been cooled to room temperature. PACKING AND STORAGE OF DEHYDRATED PRODUCTS Keeping quality of dehydrated products is dependent, to a considerable extent, on their final moisture content. The lower the moisture content, the better the keeping quality. After drying, fruits and vegetables will take up moisture from the surrounding air if allowed to remain exposed for any length of time. This absorption

13 HOME FRUIT AND VEGETABLE DEHYDRATION 13 takes place rapidly on days when the natural humidity of the air is high. To avoid absorption and to improve keeping quality, store under moisture proof conditions immediately after drying. The best types of containers for dehydrated products are glass jars with tight seals such as rubber rings, composition gaskets, or the like. If the jars have been previously used for coffee or vegetable oils, it is extremely necessary to clean them well to remove all traces of odor that might contaminate the dehydrated products. Dried vegetables such as carrots are quite susceptible to flavor changes and foreign odors. Figure 7. containers that can be used for proper storage of dehydrated vegetables. All these containers can be made airtight. Cans with tight seals or heavily waxed fiber board containers that are moisture proof can likewise be used. It is imperative, however, that any type of container used must be sealed to prevent air leakage. The addition of the better grades of sealing tape will further prevent the entry of moisture. Air leakage means moisture absorption and the possibility of insect infestation. Before placing the freshly dehydrated products in containers, be sure that the cans, jars, or containers have been thoroughly dried out by heating in an oven. Place the freshly dehyilrated product in the hot or stillwarm container. Fill the containers as full as possible and use smaller containers to avoid opening and exposing large batches of dehydrated fruits or vegetables.

14 14 AGRICULTURAL EXPERIMENT STATION CIRCULAR 149 Large tin cans with airtight covers can be used to store many small vapor-proof cellophane packages. These small packages should contain a complete serving for the family. Use of small packages best preserves the product against breakage and moisture absorption. Removal of a bag for serving, therefore, is a simple procedure and avoids damage to the balance of the food material stored in the can. Cool storage is essential for long keeping of packaged dried material. PREPARATION OF DEHYDRATED FOODS FOR COOKING Some dehydrated foods benefit by preliminary soaking, while others, especially the green, leafy vegetables, refresh during cooking. The size of the pieces determines, to a large extent, the length of time for soaking. The larger pieces take up the water more slowly, while the smaller pieces, such as shreds, dices, slices, etc., have more surface per unit volume for absorption of water and refresh more quickly. If a food is left to soak too long, it may become waterlogged and produce an unattractive product when cooked. Peaches soaked 24 hours, then cooked, do not have the attractive shape, firmness, or flavor of peaches soaked only 12 hours before cooking. Fruits can be soaked over night without spoilage, but dehydrated vegetables, if allowed to soak more than 2 hours, may show evidence of spoilage. To refresh dehydrated carrots or cabbage to be used as a fresh product in preparing salads, soak over night in a refrigerator or ice box to prevent spoilage. Foods that have been soaked should be cooked in the water in which they were soaked. Just enough water should be used to allow for refreshing and for cooking. As the majority of vegetables have been precooked or ed before drying, they will not require as long to cook as fresh vegetables. This will depend on the stage of maturity at the time the vegetables were dried. When soaking and cooking, use 1 to 2 measures of water for every measure of dehydrated vegetable with the exception of green, leafy vegetables. Cook all foods until tender. The foods may be soaked in the container in which they are to be cooked. More water can be added before cooking, if needed. Table 3 gives the amount of water, time of soaking, and time of cooking for some common dehydrated foods. These figures will vary with the style and size of cut and maturity of the product when dehydrated.

15 HOME FRUIT AND VEGETABLE DEHYDRATION 15 For example, the pumpkin was shredded before dehydration and after being dried was put through a food chopper and ground almost to a powder. The powdered vegetable takes up less space than shredded and is easy to use for making pies and custards. The reconstituted or refreshed foods may be used in the same manner as fresh-cooked foods-buttered, creamed, sautéd, pickled, etc. Cabbage and carrots refreshed over night in a refrigerator or ice box without cooking can be used in salads. Onions to be used as flavoring may be powdered and a bit of powder added as seasoning to foods without refreshing. If onion slices are wanted, the slices should be soaked for 15 minutes in water, then simmered gently for 20 to 30 minutes. One tablespoon of onions will need 3 tablespoons of water for refreshing. Dehydrated foods that have been properly prepared make attractive and flavorful dishes on reconstitution. Table 3. APPROXIMATE AMOUNTS OF WATER IRCESSARY FOR REFRESHING FRUITS AND VEGETABLES Product Peaches Pears Prunes Raspherries..._._, Rhubarb Strawberries. Asparagus Beans (snap or green) Beans (Lima) Beets (shredded) Broccoli Cabbage (shredded) Cabbage (red) Carrots (shredded) Celery Corn Parsnips Peas Peppers.., Potatoes (Irish) (Julienne) Potatoes (Sweet) Pumpkin (shredded) Pumpkin (ground fine) Rutabagas Spinach Squash Swiss chard... Tomatoes Turnip... Weight per cup Ounces Apples 2.3 Apricots (packed) 7.0 Cherries 7 Cranberries 2.0 Reconstitution proportions Volume of dehydrated Volume of Time of Time of product water soaking cooking Cups Cups hr hr hr. 5-6 hr hr hr hr hr mm hr mm mm mm mm mm none none mm mm mm mm mm Tblspn. 2 Tblspn. 30 mm mm miii mm none mm none mm. io none none mm. 10 Minutes Till tender

16 Table 1. DIRECTIONS FOR PREPARING AND DEHYDRATING FRUIT Spread Approximate yield per from 100 pounds Treatment before square of fresh malertal Approx- Dehydrated product dehydration foot of Dehydra. imate Stage of - tray Dehydrated perature time when dry tion teni- Product maturity drying Condition Preparation Keeping Method Time surface Prepared quality App1es. Firm ripe Peel, core, slice or cut in Sulphur eighths; light brine dip protects color of fruit while handling hours Apricots Firmripe Cutinhalves; remove pit Sulphur 1_1 hours Berries Firm ripe Carefully spread on trays to pre- None None vent bleeding Sweet and sour Well Pitted sweet or sour cherries Sulphur hour pitted cherries ripened dry quicker than unpitted. Spread carefully on tray Unpitted Cranberries Full ripe Whole or chopped; chopped dry None None best Peaches Full ripe Cut in halves; remove pits Sulphur 11 hours Pears Firmripe Cutinhalves;core Sulphur 1 hours Prunes Full ripe Whole or halved prunes can be None al- hour dried. Pitted fruit dries more though a rapidly light sulphuring can be used Rhubarb Mature Trim, wash, cut In slices inch 2-4 thick minutes Wherever possible, freeze or can fruits. Pounds Pounds Pounds Hours Springy Leathery Good I Springy Good 1 Pitted Pitted Leathery Tjnpitted tiripitted Brittle Good Leathery Good Leathery Good Good Good Pliable Good U Tough Good

17 Table 2. DIRECTIONS FOR PREPARING AND DEHYDRATING VEGETABLES Spread Approximate yield per from 100 pounds Dehydrated product Treatment before square of fresh material Approxdehydration foot Dehydra- imate Keep- Stage of of tray Dehy- tion tern- drying Condition ing Product maturity Preparation Method Time surface Prepared drated perature time when dry quality Asparagus Beans (green) Beans (Lima) Beets BroccolL... t Cabbage tcarrots. Celery Tender tips; stalks soft not woody Mature, tender, not stringy Tender, immature Good for table use Good and succulent Good and succulent Medium sized, succulent Medium sized, succulent Wash, trim, cut into 1k" lengths; split large pieces Snip, cut into 1-inch lengths Shell, wash Wash, trim and cook for 15 mm., peel, slice or strip inch thick Trim, wash, and slice lengthwise Trim, core, and wash. Cut in inch shreds Wash, peel, trim. Cut in slices or strips Wash, cut stalks into thin slices. Dry leaves separately for soup Corn Milk stage Husk, wash, cut from cob after ing or boiling water Boiling water Wherever possible, freeze or can vegetables. 1 Store for use during fall,or early winter. Spoilage will be reduced and qual it retained if these vegetables are dried for use in late winter anspring months. Minutes Pounds Pounds Pound.i Hours Brittle Good Greenish black Brittle Good Greenish black Hard Good Wrinkled Brittle Good Brittle Good 4S Brittle Good Brittle Fair Brittle Good S Brittle Good

18 Table 2. DIRECTIONS FOR PREPARING AND DEHYDRATING VEGRTABLE5"Continsied Spread Approximate yield per from 100 pounds Dehydrated product Treatment before square of fresh material Approx dehydration foot of Dehydra- irnate Keep- Stage of tray Dehy- tion tern- drying Condition ing Product maturity Preparation Method Time surface Prepared drated perature time when dry I quality Mmutes Pounds Pounds Pounds Hours tonlons Mature Trim, remove outer leaves, None None Brittle Good succulent wash, slice Inch thick tparsnlps Mature, Wash, peel, trim. Cut In inch Brittle Good tender not Slices or shreds woody Peas (Sugar) Full Pod and wash Hard Good grown but Wrinkled not hard Brittle or overripe tpotatoes Proper Peel, trim, wash, cut into shreds, t Pumpkin condition for table use Good table condition inch slices or strips Peel, seed, wash and shred Spinach or Good table Cut off roots: wash and sort or Greens condition water Sweet Potatoes. Good table Trim, peel, wash; slice in 2-3 condition inch slices or strips Tomatoes Good, firm Light, peel, core; cut into 2-3 table type incl slicos only ttqrnips or Rutabagas Good table condition Trim, pee], wash, slice, strip, or shred Hard Good Brittle Tough Good Brittle Crisp Good Brittle Hard Good Brittle Tough Good Brittle Tough Good Brittle Wherever possible, freeze or can vegetables. t Store for use during fall or early winter. Spoilage will be reduced and qualit retained if these vegetables are dried for use in late winter and spring months.